Nanostructured Solar Energy Devices

DR. ARNEL SALVADORProgram LeaderCondensed Matter Physics LaboratoryNational Institute of PhysicsUniversity of the Philippines, Diliman

This program is a collaboration betweenCondensed Matter Physics LaboratoryNIP – UP Diliman• Dr. Arnel Salvador• Dr. Roland Sarmago• Dr. Armando Somintac

Ateneo de Manila University• Dr. Erwin Enriquez

The program addresses various aspects and issues which affect the performance of solid-state and dye-sensitized solar cells.

Nanostructured Solar Energy Devices

Funded by DOST PCIEERD, 2010-2014

LIGHT ENERGY

• Light induces the production of electron-hole pairs (charge carriers)

•Charge carriers flow to metal contacts and produce current

The Solar Cell

• Reflection losses

• Shadow loss

• Collection efficiency

back contact reflection

top surface reflection

Shadow effect due to metal

contacts

Issues on solar cell performance

Wikimedia Commons

The Solar Spectrum

Inefficient light trapping due to reflection at the front surface

Solution:

• Surface modification (nanostructures)

• Anti-reflection coating (ARC)

Reflection loss account for roughly 30% of the optical loss in silicon solar cells

Anti-reflection coating and surface modification reduce the reflectance of silicon by 70-90%

Reflection Losses

Si

Etchantsolution Si

Textured silicon

untexturedsilicon

Increasedphotocurrent

Ph

oto

curr

ent

(a.u

.)

5 μm

% R

efle

ctan

ce

decreasedreflectancefor increasing texture time

Silicon nanopyramids by chemical texturing

Nanostructures: Textured silicon

2 μm

Silicon nanowires

Bare silicon

decreasedreflectance

% R

efle

ctan

ce

Silicon nanowires (SiNW)by metal-assisted electroless etching

Etchantsolution Si

Si

Depositmetal Si

Bare silicon

Silicon nanowires with silver nanoparticles

Silicon nanowires

Increasedphotocurrent

Ph

oto

curr

ent

(a.u

.)

Nanostructures: Silicon nanowires

Textured Si

ZnO coat

5 μm

ZnO Anti-Reflection Coating

Zinc oxide (ZnO) deposited on textured silicon

decreasedreflectance

Textured ZnO

Bare silicon

Textured Si with ZnO

% R

efle

ctan

ce

Typical solar cell

Metal contacts block 10-15% of the area available for light collection

Transparent conducting oxides

Shadow Loss

GLASSFTO

on GLASS

Highly transmitting ~80% transmission in the visible region

FTO

batteryLED

500 nm

Fluorine-doped tin oxide (FTO)

Dye-sensitized solar cell (DSSC) structure

Modified graphene as TCO(FTO-graphene nanocomposite)

Graphene sensitizer(mesoporous TiO2 with Ru-based dye)

Solid-phase electrolyte(Perovskite)

C-based counter electrode

10-12% efficiency

FTO-graphene nanocomposite for DSSC

GaAs-based solar cells

Silicon solar cells

DSSC

GaAs-based solar cells

GaAs-based solar cells

Single-junction thin film GaAs solar cell

Riber32 Molecular Beam Epitaxy

Fabricated GaAs-based solar cell

Mask AlignerMetal Deposition

GaAs-based solar cells

GaAs solar cell

23.5%efficiency

Current world record: 28.8% (Alta Devices)

Metal contacts on GaAs solar cell

GaAs-based solar cells

LED array powered by the fabricated GaAssolar cell under a sun simulator

VIDEO

GaAs-based solar cell -Demonstration

National Solar Cell Characterization Facility at NIP

Our work on nanostructures will also be utilized in other disciplines and applications in the future:

• Biosensing

• Alternative energy (Thermoelectric and Piezoelectric devices)

• Lab-on-a-Chip (LOC)

• Emerging optical and spectroscopy techniques

Terahertz spectroscopy

Multi-spectral imaging

Other studies

Textured silicon (porous Si, Si nanowires, pyramid)

p-type silicon (substrate)

Spray pyrolysis (phosphorus or doped ZnO)

n-type layerp-type substrate

Silicon solar cell

Doping techniques for silicon

IV-curve for pn-junction produced using spray pyrolysis

Metallization Techniques

In-house fabricated masks for metallization of macroscopic devices

Nanolithography for other optoelectronic devices (WYKO images)

Karl-Suss mask aligner

Metal-oxide nanostructures for ion-sensing applications

Copper oxide (CuO) nanowiresby thermal oxidation

Zinc Oxide (ZnO) nanowiresby chemical bath deposition

Nanostructures provide larger surface areas for adsorption, thus increasing the sensitivity of metal-oxides making them suitable for ion-sensing applications.

2 μm

500 nm

ChemicalBath deposition

ZnO seed layer

Cu foil

Heat

500 nm

Human Resource DevelopmentWe have trained people capable in the growth, fabrication and characterization of solar cells

GRADUATE STUDENTS in the industry: > 15 MS graduatesRECENT Phd Graduates: 3 graduatesCURRENT GRADUATE STUDENTS, MS and PhD: > 30 students

Various Facilities for Growth, Characterization and Fabrication